Who says a speaker needs a box to have a good bass response? The Katana-M1 DIY speaker kit from Monacor seemingly proves the opposite. It’s an open baffle design and I decided to build this kit to get some experience with how its special radiation pattern would sound in my room, as well as get a chance to work with my hands a little, as it was a while ago since my last speaker project. In this post I will share details about the building process, measurements, and listening impressions.
A regular box speaker tends to give an omnidirectional radiation pattern below around 500 Hz, where the wavelength is larger than the dimensions of the speaker. When placed in a large living room, the result is that reflected sound tends to have considerably more energy than the direct sound from the speaker. The audible impression of too strong reflected sound energy can be to smear the sound in the time-domain, so that the sound becomes indistinct and recorded reverberation may be masked by the reverb of the reproduction room.
An open baffle design, on the other hand, approaches dipole directivity at low frequencies. Sound is cancelled to the sides of the speaker due to the acoustic interference between the sound from the front and back of the drivers. A dipole radiation pattern gives relatively less reflected energy to the listener, and I wanted to know if the Katana M-1 speaker has an audibly more articulated low-frequency response in my living room compared to my previous regular box speakers.
Here are the finished speakers in my living room:
Building Process
The kit consists of dual 8″ woofers crossed over at 250 Hz to a 3″ full range driver, and ships with everything necessary to assemble the speakers except basic tools Link to the kit at Monacors webpage.
The kit ships with untreated wood parts, and it is up to the builder to decide on a suitable finish.
Here I experimented a bit and made a couple of mistakes before I arrived at the final design. The baffle is made out of beech. Initially I tried to apply teak oil to improve lustre, but it gave the wood a darker and somewhat greasy look. So instead I applied a colored oil with white pigment, and finished off with a hardwax oil to get a bit of lustre. I think the result is really nice.
I initially tried to spray paint the MDF side panels, but quickly found that the MDF just absorbed the paint like a sponge and I couldn’t get it to cover well (even though I applied a spray primer underneath). Luckily, I had a bucket of white water-based indoor paint that worked great on the MDF. Finally I glued everything together and used a glue gun to attach the wiring and crossover components at the back of the speaker.
Measurements
Let’s have a look at some measurements before discussing listening impressions. I measured the in-room response of the speaker using custom MATLAB scripts and a miniDSP UMIK-1 microphone. It is interesting to compare the result between the Katana M-1 and my previous DIY regular 2-way box speakers, which are depicted below. Firstly, I was a bit surprised that the Katana M-1 open baffle design has a bass response that is almost as extended as my previous speakers, which are a ported design (fc=44Hz) with a 5.25″ mid/bass-driver. The below graphs shows the response at the sweet spot, with 1/8-octave smoothing.
The Katana M-1 has a pronounced peak in the response around 2 kHz. This makes it highly recommended to apply additional EQ to get a decent spectral balance. An interesting observation is that the response peak seems to only be present in the reflected sound and not in the early direct sound (<2ms). Note that the falling response in the treble is partly due to that I didn’t use microphone calibration.
I applied Dirac Live room correction to the speakers to equalize the in-room response. This effectively compensates for the peak at 2 kHz. Before/after curves:
Okay, last measurement now. The below graph shows the energy decay between 100 to 300 Hz in my room, comparing the result for the “Dipole” Katana M-1 speaker and the regular 2-way box speaker. Indeed, the dipole characteristics of the Katana M-1 in this frequency range leads to a more distinct direct sound with a couple of dB less reflected sound. At higher frequencies however, the energy decays of the two speakers are rather similar (except around 2kHz as mentioned above). The 3″ driver of the Katana M-1 has a narrower dispersion at high frequencies than the 1″ tweeter of the 2-way box speaker, but the back-radiation of the 3″ driver partly compensates for this to give a similar energy in the reflected sound.
Listening Impressions & Conclusion
Finally, how about the sound? The Katana M-1 presents a wide soundstage, and I believe the extra articulation that the dipole design brings in the upper bass/lower mid-range makes it a bit easier to hear the recorded space separately from the reproduction space. The soundstage is rather laid-back, a bit more than I’d like personally. I would not classify this as a high-end speaker design with the response peak at 2 kHz and the related jump in direct-to-reflected sound ratio. However, the kit was fun to build, looks great and it has a relatively low price. It also gave me some ideas for future DIY speaker projects.
The real potential started to show when I added a center speaker, two subwoofers, and a pair of surround speakers together with the latest Active Room Treatment (ART) technology from Dirac, plus a not-yet-released stereo upmixing technology. But that is a topic for another post. 😉
